The present invention generally relates to recording mediums for recording and/or reproducing apparatuses, and more particularly to a hollow and substantially cylindrical-shaped recording medium suitable for use in an image pickup recording and/or reproducing apparatus such as a so-called electronic camera.
Recently, in addition to efforts for reducing the size of a video signal magnetic recording and reproducing apparatus (so-called video tape recorder, and hereinafter simply referred to as a VTR), attempts have been made to reduce the size of an image pickup camera by combining a solid-state pickup element such as a charge coupled device (CCD) with integrated circuit (IC) technology. That is, a compact and light-weight apparatus referred to as an electronic 8 mm device, unitarily comprising the VTR and the camera, has been proposed.
The above electronic 8 mm device has an advantage over the so-called conventional 8 mm movie camera using an optical 8 mm film, in that the picked up and recorded information can be reproduced on a television receiver immediately after the recording. In addition, the above electronic 8 mm device employs a magnetic tape using a metal-particle type magnetic material formed by a new magnetic layer forming technique, and a metal type head, to realize a greater recording density compared to the recording density of the conventional VTR, and the overall size of the whole device is reduced. The electronic 8 mm device essentially employs the recording and reproducing principle of a helical scan type VTR using a magnetic tape and rotary heads. Accordingly, although the electronic 8 mm device can carry out uninterrupted recording of moving pictures, without replacing once loaded roll of medium, longer than that of the 8 mm movie camera, the electronic 8 mm device has the following disadvantages.
(1) Normal recording of the moving pictures can be carried out, but a so-called still-picture-frame recording in units of fields or frames cannot be carried out.
(2) In relation to paragraph (1) above, recording in terms of picture frames wherein some randomly selected frames are replaced by new frames, and a randon access reproduction, cannot be carried out.
(3) A rotary drum provided with video heads, a tape loading mechanism for drawing out the tape from a tape cassette and loading the tape unto a predetermined tape path, a tape travel driving mechanism for causing the tape to travel through the predetermined tape path, and the like, are essential to the electronic 8 mm device, and it is difficult to achieve substantial reduction in size and weight of the mechanical structure.
(4) The limit of the track pitch upon high density recording is in the order of 20 .mu.m from the practical point of view because the tape slightly deviates upwards and downwards while traveling on the tape path, and there is a limit in the size reduction of the electronic 8 mm device due to the fact that fine quality recording and reproduction cannot be maintained if the track pitch is further reduced.
(5) It is difficult to obtain tracking by swinging technology of the rotary heads, because the track pitch is narrow as described above.
On the other hand, a so-called electronic camera which records the video signal onto a single side of a flexible magnetic disc, has been proposed as a potential replacement of the still picture camera using an optical 35 mm filter. In this electronic camera, a magnetic disc having a diameter in the order of 35 mm, for example, is rotated at a rotational speed of 3600 rpm within a main camera body having a size in the range of a normal 35 mm single-lens reflex camera. The video signal obtained by picking up an image by a solid-state pickup element such as a CCD is recorded magnetically onto the magnetic disc by a magnetic head. The magnetic head carries out recording in terms of one field for one revolution of the magnetic disc, and is successively moved along the radial direction of the magnetic disc. However, this electronic camera also suffers the following disadvantages.
(a) Because the magnetic disc is used as a recording medium and the picture of one picture frame is recorded for one revolution of the magnetic disc, the magnetic disc is rotated at a constant angular speed. Hence, the relative linear speed between the magnetic head and the magnetic disc becomes smaller towards the inner periphery of the magnetic disc. Thus, in order to carry out recording in a normal manner, the central area of the magnetic disc is unusable and wasted, and the recording range is accordingly limited. On the other hand, there is a limit to the diameter of the magnetic disc because the size of the main camera body is limited. Therefore, the effective recording area of the magnetic disc cannot be made large, and the recording capacity thus cannot be made large.
(b) In relation to paragraph (a) above, the picture quality of the recorded picture becomes poor towards innermost part of the disc whereat the relative linear speed between the magnetic head and the magnetic disc is small.
(c) A standing wave is likely to be introduced at the outermost periphery of the rotating magnetic disc because the magnetic disc comprises a flexible magnetic sheet such as a floppy disc. Hence, a flutter phenomenon may be observed on the magnetic disc due to the above standing wave, and the magnetic head cannot make stable contact with the magnetic disc. As a result, the outermost peripheral part of the disc which is most usable. whereat the relative linear speed between the magnetic head and the magnetic disc becomes large, cannot be utilized.
On the other hand, a concept was conventionally known to construct a recording and reproducing apparatus which uses a cylindrical-shaped rotary magnetic drum as a magnetic recording medium. In this apparatus which uses the magnetic drum, the relative linear speed between the magnetic head and the magnetic drum is constant regardless of the position of the magnetic head. However, the size of the recording and reproducing apparatus becomes large, because the recording capacity of the magnetic drum is not as large as the magnetic tape, and the size and volume of the magnetic drum is large. In addition, the handling of the magnetic drum is troublesome since the entire cylindrical surface of the magnetic drum is magnetic. Moreover, it is difficult to manufacture a magnetic drum comprising a good quality uniform magnetic surface. Therefore, the magnetic recording and reproducing apparatus using the magnetic drum was not reduced to practice, for the above described reasons.